As disclosed in, for example, JP-A-2003-137111, multiple wiring systems are typically used in a power supply circuit or a signal detection apparatus. Each wiring system has the same function to provide redundancy. Thus, even when some of the wiring systems are broken, the power supply circuit or the signal detection apparatus can operate normally.
Examples of faults in a power line include an earth (ground) fault in addition to a break fault. The earth fault means that an electric current flowing through the power line flows to the earth due to the fact that the power line is electrically connected to the earth.
For example, in FIG. 6, each Hall IC is supplied with electric power through two power lines PL11 and PL12. In such a case, if the power line PL12 is connected to the earth at a point EF, an electric current flowing through the power line PL12 flows to the earth from the point EF. Further, since the power line PL11 and the power line PL12 are electrically connected together, an electric current flowing through the power line PL12 also flows to the earth from the point EF.
As described above, in a power supply circuit or a signal detection apparatus having multiple power wiring systems, the power wiring systems are electrically connected together. Therefore, when an earth fault occurs in one power wiring system, the other power wiring systems may be affected by the earth fault.